In continuing efforts to automate manufacturing steps and to increase productivity, the prior art has developed a number of control systems for manufacturing operations which vary from the simple to very complex. Many of these have included sensing devices to record the status of the operations at various time intervals and locations and to provide data to a controller such as a computer or other type of timing and sequencing device. In many automated assembly procedures, one of the tool or the work piece is moved through a sequence of work stations or locations where the programmed operation is carried out. With increasing throughput speeds, one difficulty that arises involves the misalignment of one or more of the sensing devices which causes work slowdown or even stoppage to allow realignment to be effected. Another difficulty arises particularly with optical sensing devices where occlusion of the optical path occurs which requires clearing of the optical path with its attendant delays.
In complex operations such as those involving the feeding of a part at a precise time to a work site, proper functioning of the sensing devices is often critical to safe and effective operation of the tools and conveying system being controlled. However, the speed of operation and the character of the operation such as, for example, reciprocating motion of a tool member, often results in significantly increased costs in installing the control system to ensure a sufficiently long operational run before resetting or adjustment is mandatory. Where optical sensors are employed, in some of the prior art arrangements, either a photocell or a light reflecting member has been placed on a tool moving member. In article conveyors, it has been the practice to place such sensing elements adjacent the path of a member that is to be fed to a tool to control the feeding sequence. In both circumstances, frequent resetting, clearing, cleaning and adjustment of the sensing devices are necessary. As an alternative to avoid the loss of production time, reinforcement of the work station implements to minimize the occurrence of misalignment of the sensing devices has been proposed or automatically operated realignment backup systems have been employed. In either case, the increase in cost, particularly where heavy machinery is being operated, has been a significant disadvantage. In some arrangements, increased expense has been encountered due to the requirement of modifying the tools and conveying systems to enable these elements to accommodate the sensing devices.